Linear electric servo motor actuated screw thread tapper

ABSTRACT

An all electric screw thread tapper comprises an electric servo rotational motor ( 20 ) controlled as to shaft position, velocity and acceleration in combination with a linear electric servo motor ( 16 ) controlled as to armature position, velocity and acceleration. With motion controller and built-in high speed processor controls, the parameters for each job or part can be touch screened in.

BACKGROUND OF THE INVENTION

The field of the invention pertains to industrial high production screwthread tapping machinery, and, in particular, to tappers thatautomatically extend and retract as fixtured work pieces momentarilystop at the tapping station.

Currently, in conventional tappers, some of which technology dates backto the 1930's, reversible cyclic rotational motion of the tap isprovided by an electric, pneumatic or hydraulic motor. Linear reversiblemotion of the tap is provided by a pneumatic or hydraulic cylinderactuator or a leadscrew or ballscrew actuator. In many high productionsettings, the tapping time reduces throughput creating a bottleneck andmaterial handling, storage, and space problems. Therefore, the tappingtime determines overall production rate because other production stepstake less time.

The linear, pneumatic or hydraulic actuators have been found to requirevery frequent repair and replacement of mechanical components andcontrol valves to avoid unacceptable scrappage rates and customerrejections. In particular, fluctuations in plant air supply flow ratesand pressure will throw off previously properly set parameters for aspecific threaded hole. Also, the leadscrew and ballscrew systems areknown to wear and produce improper feed rates. The fluctuations causeinconsistencies in thread quality, rejection of parts already shipped tocustomers under just-in-time schedules, quarantine of the shipped parts,expedited and certified replacement parts under 100% inspection, andunacceptable costs for each rejection to the manufacturing companies. Inaddition, tool life is considerably diminished due to improper feedrates.

With some conventional tapping equipment, new set-ups for a new part ora new run of a previous part result in scrappage of hundreds of partsjust to obtain repeated gaging that meets thread specifications. Withsome models of tappers, one to four hours are required to changeleadscrews for a change of pitch. Where several changeovers or newset-ups are required per day, costly skilled worker time and lostproduction time result. When production is at the rate of a few secondsor less per tap, lost production can be many thousands per day.

In addition, conventional tapping machines have features that interferewith quick changeovers and quick tap changes. With a view towardminimizing set-up and changeover time, quality rejections, frequentmaintenance due to fluctuations in air flow and pressures, leadscrewerror and ballscrew error, the following improvements have beendeveloped.

SUMMARY OF THE INVENTION

The invention comprises the elimination of mechanical, pneumatic orhydraulic actuators or motors and outdated controls by replacement withelectric servo motors and state-of-the-art controls, in particular, forlinear movements. Modem rotational electric motors, such as servos and“stepper motors,” can be very carefully controlled not only as torotational speed and acceleration but also as to rotational position.Likewise, linear electric servo motors (actuators) now can be veryaccurately controlled as to armature speed, acceleration and positionwith feedback from a built-in encoder, drive output signals, and motioncontrollers. In addition, this machine can monitor and display feedbackfrom current load on the spindle in real time with adjustable ranges foreach job stored in memory, and with each job to turn the machine off andsend a message to the display for the operator to change the tool. Theservo tapper disclosed below results in a significant number ofimprovements in the tapper, partly by simplifying the overall mechanism.Costly downtime due to work clutches, damaged gears, worn belts orpulleys, worn leadscrews and leadscrew changeovers, ballscrew wear andreplacement, and hydraulic seal leaks and spillage are eliminated. Tapchanges in excess of 45 seconds, and other excessive changeover timesdue to many adjustments, are also eliminated.

Further improvements arise from the elimination of quality problems dueto Jacobs tapper runout and mounting problems, double tapped or reamedholes, partially tapped and untapped holes caused by improperadjustments to limit switches which are manually adjusted, and out ofspecification threads from fluctuating air or hydraulic pressure orleadscrew or ballscrew error.

With the linear electric servo motor, and the encoder feedback,substantially all the tapping parameters can be pre-programmed andmonitored through a motion controller with a built-in high speedprocessor through a touch screen interface. For example, in thepreferred embodiment, all tapping parameters are programmed through thetouch panel with very user-friendly screens, and a self-teach feature toestablish depths has been added for first time set-up and job storagefor up to 700 different job set-ups, each with up to 15 differentparameters. As a result, with a touch screen panel, there are quick jobchangeovers, programmable depths, quick change taphead retract featuresand tap RPM in and RPM out (up to 7,500 rpm's) separately selectable forreduced cycle time all without manual adjustments. Moreover, tap pitchescan be programmable slave driven from a master spindle (meaning if youincrease the RPM in either direction, the feed rate automaticallycompensates to match tap pitch requiring no adjustments to maximize toollife and throughput). Also, this machine has a rapid advance feature toclear the tool for indexing of the parts when required.

Despite the simplification accomplished by using a linear electric servomotor, the new tapper is not limited as to vertical, horizontal orangular orientation or multiple spindle heads. With a reliable directdrive, very accurate rotational electric servo motors, and linearelectric servo motors, increased tool life from exact feed rates andmuch faster cycle times than competitive machines are achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the new tapper complete with an angularbase;

FIG. 2 is an end view of the new tapper complete with an angular base;

FIG. 3 is a plan view of the new tapper complete with an angular base;

FIG. 4 is a perspective view of the complete tapper with explodedmounting plates or retrofit;

FIG. 5 is an exploded perspective view of the mechanical tapper;

FIG. 6 is a perspective view of the mechanical assembly;

FIG. 7 is an exploded perspective view of the mechanical assembly;

FIG. 8 is an exploded plan view of the mechanical assembly;

FIG. 9 is an exploded side view of the mechanical assembly;

FIG. 10 is a flow chart for the operator interface screen;

FIG. 11 is a picture of the main screen from FIG. 10;

FIG. 12 is a picture of the manual and jog screen from FIG. 10;

FIG. 13 is a picture of the set-up screen from FIG. 10;

FIG. 14 is a picture of the current monitor screen from FIG. 10;

FIG. 15 is a picture of the drill set-up screen from FIG. 10;

FIG. 16 is a perspective drawing of the tapper showing critical controlpanels; and

FIG. 17 is a schematic communications flow chart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated in FIGS. 1 through 9 and 16 is the new tapper on angularmount base 25. The tapper is generally denoted by 26. A fixture (notshown) having sequential part feeding means would be mounted on the base25 by means of the base sub plate 4. A fixture for retaining a part inproper position in relation to the axis of the tap 1, tool holder 18 andchuck 19 would also be mounted on the base sub plate 4.

Affixed to the upper surface of the base sub plate 4 are four guide rodmounts 7. A slide plate 2 is slideably attached by four guide rod slidemounts 6, all of which have two bushings 3 press fit for linear movementon guide rods 8. Affixed to upper side of slide plate 2 is the spindlemotor mount 12 which retains one of two double angular contact bearings9 for the spindle 11. The spindle motor mount also retains themisalignment coupling 21 inside, which couples the spindle servo outputshaft to spindle 11. The rotational spindle servo 20 is affixed to theback side of motor mount 12, and the nose piece 10, which retains thesecond double angular contact bearing, is affixed to the front side.When activated, spindle servo 20 rotates, moving clockwise to tap ordrill into a work piece and counter clockwise (except in drill mode) toretract out of work piece. Linear slide plate 2 on the under side hasaffixed to it the linear slide mount 5, which is affixed to the armaturetransition mount 15. Armature transition mount 15 is affixed to thearmature 14 of linear electric servo motor 16 which, when activated,drives the slide plate 2 linearly on the guide rods 8 while providingaccurate feed rate synchronized to the spindle servo 20 by programmedpitch coordinated with programmed rpm.

A linear motor mount 13 and encoder 17 is attached to the back of themachine base 25, unless provided as a weldment or retrofit to supportthe linear electric servo motor 16. The armature 14 passes through ahole in the linear mount 13 and attaches to the armature transitionmount 15.

The basic control functions are illustrated in FIGS. 10 through 16wherein a touch screen 24 in the operator control panel 23 permits anoperator to both set up the parameters for a new part to be tapped ormonitor tapping performance in real time for current production. FIG. 10illustrates the touch screen 24 display for a typical set-up of a newpart, as well as auto and manual modes. The motion controller in themaster control panel 22 comprises principally a micro computer withmemory sufficient for all parameters for all expected jobs or parts. Themotion controller in turn directly controls the drives to send aspecified current to the spindle servo 20 and the linear motor 16 toreach programmed speeds and feeds. The linear electric servo motor 16 isequipped with an encoder 17 to feed back armature 14 linear position,velocity and acceleration to the motion controller. Similarly, thespindle motor 20.is equipped with a resolver to feed back output shaftand spindle 11 rotational position, velocity and acceleration. Inproduction, each part can be tapped in some one-half of a second. Thecycle time can be significantly reduced by optimizing various steps asthe job is set up. For example, the rotational speed of the tap islimited by strength of the tap and heat buildup during thread cutting.During retraction of the tap, the rotational and linear speed of the tapcan be greatly increased to reduce cycle time. As shown in FIG. 10, the“RPM in” is programmed separate from that of the RPM out and can be setat speeds of up to 7,500 RPM's, thereby reducing the time to retract thetap in some cases to less than one-tenth of the tap cutting time. FIG.10 illustrates the logical sequence for an operator to program in a newpart by part number.

The operator enters on the touch screen the parameters and otherinformation in sequence, as shown in the flow chart. In FIG. 10, nomechanical adjustments are required, unless the new part requires achange in the tooling fixture or a change in the tap. In the new partset-up, the computer program computes internal parameters, such asnumber of tap rotations and linear travel per rotation, from theparameters entered by the operator on the touch screen 24.

The basic control functions are illustrated in FIG. 17 wherein the touchscreen 24 permits an operator to both set up the parameters for a newpart to be tapped or monitor tapping performance in real time forcurrent production. As noted above, the motion controller 30 comprisesprincipally a micro computer with memory sufficient for all parametersfor all expected jobs or parts. The motion controller 30 in turndirectly controls through drive amplifiers 32 and 34 the linear electricservo motor 16 and the spindle electric servo motor 20.

1. A thread tapper and drill machine comprising a servo spindle motorand spindle, at least one mount supporting the spindle motor andspindle, said mount supported on means on abase to provide for linearlyguided movement of the spindle motor and spindle relative to the base,and means on the spindle for axially attaching a tap thereto, theimprovement comprising an electric linear servo motor mounted on saidbase, said electric linear servo motor having an armature, the armaturehaving at least one end, the end attached to the at least one mount ofthe servo spindle motor and spindle, whereby the spindle motor canimpart controlled rotational movement to the spindle and the linearelectric motor can impart controlled axial movement to the spindle.
 2. Athread tapper comprising a spindle, an electric rotational servo motorto impart rotational movement to the spindle, an electric linear servomotor to impart linear movement to the spindle and means on the spindleto attach a tap thereto, a motion control computer in electricalcommunication with the rotational servo motor and linear servo motor, atouch screen and a memory in electrical communication with the computer,and software installed in the computer to respond to set-up parametersfrom the touch screen, including linear extension and retraction limits,number of rotations, linear speed and rotational speed.
 3. The threadtapper of claim 2 wherein the software includes a production mode forcyclic operation of the tapper and real time monitoring on the touchscreen of the production mode.